1. Field of the Invention
The present invention relates to a front end device that is connected between a transmission-reception apparatus and an antenna and that performs certain processing on a high-frequency signal.
2. Description of the Related Art
Mobile communication terminals, such as cellular phone terminals, supporting multiple communication methods and frequency bands are in widespread use in recent years. Many semiconductor components including switch integrated circuits (ICs) and power amplifier ICs are mounted on front end devices used in such mobile communication terminals. In order to support the multiple communication methods and frequency bands, the number of semiconductor components mounted in each front end device tends to increase. Such front end devices include, for example, a front end device disclosed in Japanese Unexamined Patent Application Publication No. 2012-501614. The front end device described in Japanese Unexamined Patent Application Publication No. 2012-501614 includes multiple switch ICs and power amplifiers in order to support the multiple communication methods and frequency bands.
The semiconductor components used in the mobile communication terminals, such as the cellular phone terminals, have hitherto been controlled by a parallel transmission method typified by General Purpose Input/Output (GPIO). However, the semiconductor components used in the mobile communication terminals tends to be controlled by a serial transmission method typified by Mobile Industry Processor Interface (MIPI) in order to meet a request to reduce the number of wires, a request to reduce power consumption, and so on. A system using the serial transmission method is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2009-141561. In a mobile communication terminal described in Japanese Unexamined Patent Application Publication No. 2009-141561, control signals for a semiconductor device are subjected to serial transmission by a differential transmission method.
FIG. 3 illustrates an example of a front end device in related art using the serial transmission method. FIG. 3 is a circuit diagram illustrating a front end device 1P in the related art. Referring to FIG. 3, the front end device 1P includes five high-frequency devices 11P. Each high-frequency device 11P includes a serial-parallel interface unit (S/P I/F) 11aP and a high-frequency processor 11bP. An identifier (ID) (an identification specific number) is allocated to each of the five high-frequency devices 11P. The high-frequency device 11P is, for example, a semiconductor component, such as a switch IC or a power amplifier IC.
The S/P interface unit 11aP is connected to a serial interface unit (S I/F) 31a in a Radio Frequency Integrated Circuit (RFIC) 31 via three signal lines. The high-frequency processor 11bP is connected between the RFIC 31 and an antenna (not illustrated). The RFIC 31 receives and outputs a high-frequency signal that is received with and transmitted from the antenna and outputs a serial signal from the serial interface unit 31a to control the front end device 1P.
The S/P interface unit 11aP receives the serial signal from the serial interface unit 31a to compare ID information included in the serial signal with the specific ID. If the ID information included in the serial signal coincides with the specific ID, the S/P interface unit 11aP converts the serial signal into a parallel signal to control the high-frequency processor 11bP on the basis of the parallel signal. The high-frequency processor 11bP performs certain processing on the high-frequency signal supplied from the RFIC 31 side or the antenna side under the control of the S/P interface unit 11aP.
As illustrated in FIG. 3, it is necessary for the high-frequency device supporting the serial transmission method to include the S/P interface unit that performs the serial-to-parallel conversion. The S/P interface unit generally requires a large mounting area. Accordingly, the size of each high-frequency device that is mounted is increased in the front end device using the serial transmission method for the control of the high-frequency devices. As a result, the front end device including the multiple high-frequency devices is increased in size. In other words, since it is necessary to mount the multiple large high-frequency devices when the serial transmission method is used for the control of the high-frequency devices, the front end device is increased in size.